Dual-mode bifurcated waveguide transducer



Feb. 2, 1960 c w, CURTIS ETAL 2,923,895

DUALMODE BIFURCATED WAVEGUIDE TRANSDUCER Filed Oct. 1, 1956 Fig. 3.

INVENTORS. Charles W.Cur1is, Roben L.Foge|,

ATTORNEY United States Patent DUALMODE BIFURCATED WAVEGUIDE TRANSDUCERCharlesW. Curtis, Manhattan Beach, and Robert L. Fogel, Torrance,Calif., assiguors to Hughes Aircraft Company, Culver City, Calif., acorporation of Delaware Application October 1, 1956, Serial No. 613,0233 Claims. c1. ass-9 This invention relates to a waveguide transducer andmore particularly to a waveguide structure which permits the selectionof predetermined modes.

' In wave energy transmission systems it is often desirable to providefor propagation of more than one signal using a common frequency byutilizing various wave energy modes as separate channels. It is wellknown in theart that twqdominant modes such as the TE and the TE -modeofthe square waveguide will propagate independently because they areorthogonal. The practical problem associated with this problem is toexcite or to extract wave energy in one mode independent of the thermode. One transducer having the above indicated properties which hasbeen. used in the past to; perform thisfunction comprises a circularwaveguide to which-two rectangular waveguides are radially coupled byway of apertures. The longitudinal axes of the two rectangular 2,923,895Patented eb. 2,

ducer of this invention, a cruciform waveguide adapted to propagate thetwo orthogonal TE and TE wave and the circular waveguides are mutuallyperpendicular. a it This waveguide transducer which is fully describedin A Broad-Band Dual-Mode Circular Waveguide Transducer by R. D.,Tompkins, IRE Transaction on. Microwave Theory andTechniques,.published by the Institute of RadioEngineers, Inc., vol.MIT-4, number 3, page 181 (July 1956), involves the transformation oforthogonal TE -modes of the circularwaveguide to the dominant TE -modesof two separate and orthogonally positioned rectangular waveguides.This, as well as other prior art transducers, give rise to relativelyhigh reflections due to the non-symmetry of the junctions and lessisolation between the channels than desirable. Further, this type oftransducerrequires the excitation of an aperture, namely, therectangular opening in the circular waveguide wall to which therectangular waveguide is coupled. All sys- It is therefore an object ofthis invention to provide a waveguide transducer adapted toindependently excite or extract wave energy in two orthogonal modeswithout the use of auxiliary matching or absorption components or theinclusion of electrical short circuit terminations.

It is a further object of this invention to provide a symmetricwaveguide transducer having negligible reflection loss, a high order ofisolation, and which is capable of handling large amounts of power, bothwhen exciting and when extracting one of the modes.

It is a still further object of this invention to provide a waveguidetransducerwhich is simple in construction, has a high efl'iciency, andwhich is broad-band in operation.

In accordance with the dual-mode waveguide transenergy modes may bebifurcatedinto two rectangular waveguides each adapted to propagate adifferent one of the two orthogonal wave energy modes. Thistransducer isa device which along one direction of propaga tion separates twoorthogonal wave energy modes, and along the other direction ofpropagation combines two orthogonal wave energy modes.

Fig. 1 is a perspective end view of the bifurcated waveguide transitionof this invention, Fig. in shows the electric field vector distributionthereof;

Fig. 2 is a cutaway perspective side view of the waveguide transducer ofFig. 1; and H Fig. 3 is a cross-sectionalview taken along the line 33 ofthe waveguide transducer of Fig.2.

The novel features which are believed to be character istic of theinvention, both as to its organization and method of operation, togetherwith further objects and advantages thereof, will be better understoodfrom the following description considered in connectionwith theaccompanying drawing in which an embodiment of the invention isillustrated by way of example. It is to be expressly understood,however, that the drawingis for the purpose of illustration anddescription only, and is not intended as a definition of the limits ofthe invention. Referring now to the drawing wherein like numerals areused throughout to designate likeparts, thereare shown different viewsof the dual-mode bifurcated waveguide transducer in accordance with thisinvention. I A first rectangular 12 is curved along its direction ofelongation about its broad walls 14 and 16. A second rectangularwaveguide 20 having longitudinal axis 22 is curved along its directionofelongation about its narrow walls 24- and 26. The first and the secondwaveguides 10 and 20 are brought into coincidence with one another byremoving obstruct- 10 and 20 terminate and a'straight portion commences.

The waveguides 10 and 20 may thereforebe regarded as having lost theiridentity as individual waveguides and instead define a cruciformwaveguide 30 having longitudinal axis 32.

Whereas from a structural point of view the waveguide transducer of thisinvention may be regarded as a coinbinationof two intersectingrectangular waveguides, it, is nevertheless useful to describe thewaveguide structure from a functional viewpoint. From a functionalviewpoint, the invention comprises a cruciform waveguide 30 which isbifurcated into two rectangular waveguides 10 and 20 which are spatiallydisposed with respect to one another so that thenarrow walls of one areparallel to the broad walls of the other, and whose longitudinal axes 12and 22 define a plane.

Fig. 1a depicts the orthogonal modes which the cruciform waveguide 30 isadapted to propagate. These are respectively similar to the TE -mode andthe TE -mode of the square waveguide. This nomenclature indicates theorthogonal nature of the two modes but otherwise is a not helpful afterthe wave energy propagated through the modes will separate after passingpoint 28 so that the waveguide 10 having a longitudinal axis first andthe second waveguide and 20 each are excited in their respectivedominant mode.

The symmetry of the wave energy transducer of this invention whichresults by the bifurcation prevents any cross coupling between the modesand therefore assures ofa high degree of isolation. Further, the tworectangu lar: waveguides are excited directly, in contradistinct-ionfrom aperture excitation, which provides for better broad band:operation and large power handling capacity.

The applications which involve the employment of thedual-mode'bifurcated waveguide transducer of this invention are verynumerous as is immediately apparent to thoseskil-led in the: art.Generally, the cruciform waveguide is "coupled by standard techniquessuch as a quarter wave transformer or a tapered section to a Waveguideof more. conventional cross-section and adapted to propagate orthogonalwaveguide modes; Such conventional crosssections, of course. are squareor circular.

One application of the bifurcated transducer utilizes the property thatorthogonal modes may be; transmitted along a squareor. circularwaveguide independent of one another. It is therefore possible to effectthe excitation and the subsequent transmission of independent waveenergy signals along a single square or circular waveguide. Each of;.the two independent signals is, excited in one or the other, ofthereotangular waveguides 10 and 26. The two signals will then, bepropagated in the cruciform waveguide; 30. as; orthogonal modes. To.separate the twosigual's, a second; bifurcated wave energy: transducerma be, coupled to, the transmission system having correspondingrectaugularwaveguides either parallel or' perpendicular to the firsttransducer.

7 Another application of this bifurcated waveguide transducer involvesconventional duplexing. Here the cruciform waveguide is coupled to a 45degree rotator such as an isolator employing a ferromagnetic ceramicelement which is: subjected to a longitudinal constant magnetic field.Suc'h isolators are well known. in the. art. The combination of, thebifurcated transducer and the isolator prvide duplexing action when onerectangular waveguide is. coupled to-a transmitter, the second waveguideis cou pled toareceiver and the output of the isolator is coupled to anantenna.

Still another application of the bifurcated wave energy transducer ofthis invention is the excitation of a wave energy antenna. Suchexcitation modes include circular polarization, elliptical polarizationor plane polarization along one or two predetermined planes depending onthe respectiveamplitude and phase excitation of the, first and. secondwaveguide.

What is claimed is: t

'1'. A dual-mode bifurcated waveguide transducer com-. prising: a firstrectangular waveguide including parallel broad walls curved along itsdirection of elongation about said' broad walls and terminating in afirst straight portijoh, said first waverguide, defining a firstlongitudinal axis; and a. second rectangular waveguide includingparallel narrow Walls curved along-"its-d-irection of elongation aboutsaid narrow walls and terminating in a second straight portion, saidsecond waveguide defining a second longitudinal axis, said first andsaid second waveguides being spatially oriented with respect to oneanother so that the broad walls of said first waveguide are parallel tothe narrow Wall's of said-secondf waveguide, and coupled to one anotherby-progre's'siv'ely increasing intersection so thatsaid first straightportion and said second straight portion combine. to. providea'cruciforrn wave guide having a third longitudinal axis lying in aplane'defined by said first and said second longitudinal axes andcoinciding therewith alongsaid straight portion.

2a A waveguide transducer for coupling energy'between a common waveguidesection and twoindividual waveguide arms, the modes supported in each ofthe different individual arms and in the common section being orthogonalwith respect to eah other, said transducer comprising: a first curvedrectangular waveguidehaving planar broad walls andcurv'ed narrow walls;and a second rectangular waveguidefiliavin'g planar narrow walls andcurved broad walls, tliebroad walls" of the two waveguides lying inplanes which are normal with respect to each other, said waveguidesmerging into a common cruciform rectangular waveg'uide body defining tworectangular waveguides normal to each other and coli'near witheachother, said waveguides being I'n'erg'ed along the lines ofintersection of the walls thereof and having matching internal aperturessuch that'the interior of each waveguide is of-atl'ea'st full; crosssection and such that a central portion of each of saidwaveguides at thecommon cruciform body is common with the, other of said waveguides.

3. A dual mode bifurcated waveguide transducer comprising: a firstrectangular waveguide including parallel broad walls, curvedalong itsdirection of elongation about said broad walls, and terminating in'a-fir's't straight rectangula'r waveguide portion; and a secondrectangular wave guide including parallel-narrow walls, curved along itsdirection of elongation about said narrow walls, and terminating in asecond"straight portion, the planes of the broad walls of said first andsecond waveguides being normal with respect to each other and thedirections of curvature of the curved walls therein being opposite indirection, the straight portions of each of said waveguides beingcolinear, the, bodies of said waveguides merging into each other so thata common cruciform waveguide body is provided by the straight'sectionsof saidl'rect'angular waveguides. h v

References Cited in the file of this patent UNITED STATES PATENTSKat'zih Nov; 14, 1944 2,364,371 Katzin a- Dec. 5, 1944 2,441,574 Ja/nestle at May 1:8, 194% 2,540,839 Southworth ...e Feb. 6, 1951

